The next interesting situation occurred after Rybka played 33. h4. In the game, Stockfish played 33...f5, evaluating it at 0.00. The interesting thing is that up through the 26th ply, Stockfish saw only 34. gxf5 (0.00). On the 27th ply, Stockfish finally sees 34. g5!:

After 41. Rd2, <AK> mentioned that Stockfish should consider 41...Bxf3, believing that white's knight is more valuable than black's bishop in this closed position. Stockfish considers it, but even up through 34-ply, 41...Bxf3 is never the front runner:

After 55...Kc6, <AK> was hoping that Rybka would play 56. Bd6. Indeed, at low ply during the game, I was worried because Stockfish "saw" that move, and temporarily assigned it an eval of over 1.00. However, Stockfish gives the position this strange evaluation:

During the game, <AK> kept hoping that Rybka would find a way to advance its h-pawn. I will leave that very interesting part of the analysis to <AK> to see if he can make it work.

After 91. b4, which Rybka played apparently to avoid the 50-move rule, I went over the remaining moves carefully, looking for improvements for black. Initially, I thought 98...Rhc8 and 100...Be3 were improvements but they both petered out to 0.00. I'll not show the analysis.

I slid forward from that position to see if either side had chances. The best I can tell, the answer is no. Here is the line I found: <107.Bb4 Rc2+ 108.Kxg3 Bc7 109.Rxh8 Bxe5+ 110.Kf3 Bxh8 111.a5 Kc6 112.Ra1 d3 113.Ra3 Rh2 114.Rxd3 Rh3+ 115.Ke2 Rh2+ 116.Kd1 Rxh4 117.Rd6+ Kc7 118.Rb6 Rc4 119.Ke2 Be5 120.Rxe6 Rxb4 121.Rxe5 Kd6>

aylerkupp: I was playing the black pieces and thoughtlessly moved both rooks off the back rank. R played b3
.
kutztown46x: if we do reach 50 moves, I wonder if Yahoo will recognize it.
kutztown46x: For that matter, will my Fritz GUI recognize it?

aylerkupp: Yahoo should since we're playing the game from the start. Less sure about our GUIs.

aylerkupp: I feel like the soldiers in WW I waiting for the signal to jump out of their trenches.

goldenexecutive10: In my last game vs the masters, qilzqhynw posted: "this is a must-win game for the allies right? " What did he mean?

aylerkupp: Or the drivers at Le Mans waiting for 4:00 PM for the race to start.

aylerkupp: qilzqhynw meant that the Masters (allies) had to win in order to win the tournament.

kutztown46x: GE, he meant the humans had to win, or else the best they can do is 2nd place.

kutztown46x: only R or S can win the tournament now.

aylerkupp: 5 mins to go for me

kutztown46x: no, you must wait for 23 minutes.

aylerkupp: Oh, I thought it was 27. Then I better reset my GUI's clock.
kutztown46x: I had 37, you had 23.

kutztown46x: You can verify that on your forum.

aylerkupp: Yes, of course. You're right. Another senior moment.

goldenexecutive10: Thanks for clarifying !

aylerkupp: I hope I remember to enter the move on Yahoo once Rybka makes its first move.

kutztown46x: I'll remind you once your clock goes down to 1 minute.

aylerkupp: I cranked up the volume on my speakers just to make sure I heard the move announcement.

kutztown46x: If there is a check, it may split your eardrums.

aylerkupp: I feel like I'm watching Iron Chef America, Top Chef Masters, or some other cooking show when they count down the time remaining.

aylerkupp: Nope, I can't see any legal checks.

kutztown46x: I could play Bxe5+.

aylerkupp: Or a missile launch, 10...9...8...7...

aylerkupp: After the waiting the game itself will probably be anticlimactic

kutztown46x: really?

goldenexecutive10: Its like and adjourment game

aylerkupp: I hope I can find the spacebar when the time comes.

kutztown46x: 1 minute.

aylerkupp: I'm sure glad I have my diaper on.

aylerkupp: OK, R is calculating.

aylerkupp: And I almost missed it.

kutztown46x: OK, my turn to wait.

goldenexecutive10: I really like the sportsmanship behavior at this tournament

aylerkupp: I'll wake you with 1 min to go.

aylerkupp: It's not like it's a life and death matter.

kutztown46x: when Yahoo clock gets to about 23:05, I will start my engine and enter your move.

aylerkupp: And, besides, it's more fun this way.

kutztown46x: I meant 37:05.

aylerkupp: Yes, I was about to tell you that.

aylerkupp: Talk about good sportsmanship!

kutztown46x: It will take a little time to rebuild the hash table.

kutztown46x: on Saturday S wa@@@@@@@@@ 32-ply in seconds.

kutztown46x: why did it display that way?

aylerkupp: R was in the low to mid 20's. When you have a large hash table and are repeating moves, that's what happens.

I decided to take a break from the Team White vs. Team Black game and return to the Masters vs. Machines tournament. I was encouraged by the success of my pre-game preparation for the previous Houdini vs. Rybka game even though Rybka couldn't quite come up with the win. So I did something similar prior the Rybka vs. Stockfish game. I'm including all this trivia in case you find it amusing and shows what can happen when you have a MDOP (Meticulous, Detail-Oriented Person) Excel junkie with obviously too much time on their hands. If you don't find it amusing and/or interesting, well you were warned not to read further.

First I downloaded all the latest CCRL 40/40 Rybka vs. Stockfish games. There were a lot more games (246 total, compared with the 41 games between Houdini vs. Rybka). It was also more involved since there were multiple Rybka versions (4, 4.1) and multiple Stockfish versions represented (1.7.1, 1.8, 1.9, and 2.0.1) as well as 64-bit and 32-bit versions of both engines. Since Rybka had White and the choice of opening move, I also looked at their relative record for games starting with 1.e4 and 1.d4 (I consider any other opening moves to be for wimps), as well as Rybka 4.x's record against Stockfish 2.0.1 and the number of moves per game. The results:

So Rybka 4.x actually did slightly better against Stockfish 2.0.1 than against the combined set of all Stockfish versions, and the average game a little bit longer. So, to simplify things, I looked at Rybka's play against all Stockfish versions since this would also give me a larger statistical sample.

Looking at 1.e4 vs. 1.d4 I got the following results for Rybka 4.x against all Stockfish versions:

So clearly Rybka does much better against Stockfish with 1.e4 than 1.d4. Which pleases me since I'm a confirmed 1.e4 player. Or, as Bobby Fischer would have said, "Best by test". The average length of a game was also a little bit longer after opening with 1.e4 than 1.d4.

Now on to determining what would be the best opening and variation to use. To simplify the comparisons I calculated a Rybka/Stockfish (R/S) performance ratio where each win by an engine was worth 1 point, each draw was worth 0.5 points, and each loss was worth 0 points; then divided one engine's performance by the other engine's performance. Basically, a R/S performance ratio > 1 means that Rybka outperformed Stockfish in a given set of games and a R/S performance ratio < 1 means that Stockfish outperformed Rybka in that set of games.

As expected, the R/S performance ratio for games starting with 1.e4 was much higher than for games started with 1.d4.

The following openings gave the indicated R/S performance ratios for various openings when more than 3 games were played with that opening between the engines, with R/S performance ratios in parenthesis:

So, needless to say, I was very happy that <kutztown46> elected to play the Caro-Kann! And, of the various approaches Rybka tried against the Caro-Kann, the advance variation did best; 2 wins, 0 losses, 2 draws (R/S = 3.00). So this was the reason why I selected this variation in our actual game since I wasn't happy with the results of my old favorite, the Panov-Botvinnik attack (1 draw). This was corroborated by the results of the tournament games.

But I wanted more direct experience so, like in my preparation for Rybka's game against Houdini, I ran a series of 35 tournament games between Rybka 4.1 (White) against Stockfish 2.0.1 (Black) at a 120 min time control using selected 1.e4 openings, trying to guess what defense <kutztown46> would use. Since Stockfish needed to win in order to win the tournament, I expected a Sicilian or even a Ruy Lopez Marshall , given Houdini's less than stellar performance on the White side of a Ruy Lopez Marshal. I really didn't expect <kutztown46> to select a Caro-Kann.

The results of the tournament games were not at all what I expected; Rybka won 7/35 games (20.0%), Stockfish 8/35 games (22.2%) and 57.1% of the games were drawn. Huh? Not at all comparable with the CCRL results, and not exactly encouraging.

Maybe it was my choice of openings. Here are the results and the R/S performance ratios:

I used to play the Panov-Botvinnik attack against the infrequent Caro-Kann with good results since the isolated queen pawn suited my attacking style but the tournament games resulted in 4 draws (R/S = 1.00). I guess defensive play has gotten better. And the French Winawer, Poisoned Pawn turned to be a whitewash for Stockfish; 3 loses in 3 games. So, if you're playing White against Stockfish, open 1.e4 and hope for a Winawer Poisoned Pawn. It may be your best chance.

On the other hand, the R/S for the Ruy Lopez Marshall, main line was only 0.50 (0 wins, 2 losses, 4 draws) giving credence that engines (at least Houdini and Rybka) don't seem to know how to play the White side of a Ruy Lopez Marshall very well. So I tried various anti-Marshalls (8.a4, 8.d4, and 8.h3) and got a more respectable R/S of 1.00 (1 win, 1 loss, 3 draws). Still not what I had hoped for, but better than the various Marshalls.

But I ran out of time to run additional tournament games so I created a short table of those 4 defenses plus other "reasonable" defenses against 1.e4 (Alekhine, Robatch, Pirc, Scandinavian) and various possible lines for each. So I thought I was well prepared and ready to play Stockfish/<kutztown46>.

Golden Executive: <Then, with 1 (one!) move left before a draw via the 50-move rule applied and with 3 min, 1 sec left on its clock, Rybka played 91.b4, restarting the 50-move counter. Disaster! (I had a different expletive in mind, but I censored it)>

<What I think happened was that Rybka evaluated it's position as sufficiently better so that a draw was unacceptable, regardless of how much time was left in its clock. The least drastic way that it could avoid a draw was by a pawn move since a piece capture (by a sacrifice) would have driven its evals negative. Since it was a pawn up and the pawn would be regained within a few moves (it may or may not have seen this)>

Probably <kutztown46> was in touch with Nakamura, but at the end, <KT> was a gentleman:

Finally, enough time (probably too much time!) and motivation to comment on the game. That and some well-deserved prodding by <kutztown46>. As usual by now, I set the Arena GUI to 93 minutes/game to give me 12 minutes to deal with Clock Lag. I entered the first 8 moves myself based on my opening cheat sheet rather than allowing Rybka to play the first 8 moves. Again, the game score will be easier to read if you copy it to Word or another word processor, change the spaces to tabs, and adjust the tab setting appropriately so that the moves and stats line up in columns.

<kutztown46>'s choice of the Caro-Kann was a surprise to me since I expected him to press for a win since Stockfish needed a win in order to win the tournament. But his philosophy and approach was different as he indicated earlier. I wanted to win to guarantee first place in the tournament since the Masters were able to beat Houdini in their last game with Black and there was a possibility that they could do so again with White. I chose the advance variation because it provided Rybka with the best results in the latest CCRL 40/40 tournament as described and I wasn't satisfied with the winning chances in either the typical main line Caro-Kann or my earlier favorite, the Panov-Botvinnik attack. And my choice of the advance variation was apparently a surprise for <kutztown46>

Time to let Rybka and Stockfish go at each other. The position after 8.Nb3 was part of a line arrived at by transposition which, after 8...Bh7 provided a 50% winning advantage for White per Opening Explorer so I was satisfied with that.
<kutztown46> chose 8...a6 because it provided the best results for Black but with only 5 games in the database I don't consider that a meaningful statistical sample. And apparently Rybka was also satisfied with the position since it evaluated it slightly in White's favor.

I let Rybka take its time before making its next few moves to make sure that it didn't mess up the good position that I had given it Ί but time management is Rybka's Achilles' Heel; it takes a long time in the opening when it has time on its clock, typically leaving itself with less time on its clock at the later part of the game as compared with either Houdini or Stockfish. <kutztown46> knew this and planned to try to take advantage of it. But I figured that it was still early in the game and that I could make up the time differential later when Rybka's hash table was full and it could get to deeper depths quicker. But, as we all know by now, this didn't exactly work out well.

This I found to be the most interesting move by Stockfish. It gives up a pawn but in return it gets the two bishops plus an attack. I mentioned that it reminded me of a Ruy Lopez, Marshall Attack when Black does a similar thing although the follow-up is, of course, much different.

<kutztown46> indicated that Stockfish preferred 12.Be3 over 12.Bxh5. If given more time (almost 9 mins in Infinite Analysis mode) Rybka at d=17 prefers 12.Bxh5 over 13.Be3 by a small margin, [=0.66] vs. [+0.54]. But given an additional 5 mins and one more ply Rybka now prefers both 12.c3 {+0.54] and 12.dxc5 [+0.50] over both 12.Bxh5 and 12.Be3, both evaluated at [+0.48]. The game would have taken a very different turn if Rybka had chosen either of those 2 alternatives.

In return for his pawn Stockfish has good squares for his bishops and Rybka has locked in his bishop slightly with 17.c3. Maybe 17.Bc3 preserving the bishops freedom of movement and overprotecting the Pe5 was better, but then White has to worry about defending its Pc2. Rybka calculated for only 5 secs before selecting 17.c3 so it must have decided on it while it was spending all that time on moves 9  14.

After 17.Bc3 Black also has the possibility of 17...Be4 followed by 18...Bxf3 19.Qxf3 Qxf3 20.gxf3 Rxh3 regaining the pawn with the better position, so maybe this was what Rybka was trying to prevent. Instead, Stockfish's next move forces Rybka's KR to go where it probably wanted to go anyway.

<kutztown46> indicated that Stockfish preferred 19.Qa4+ followed by 20.Qg4 and exchanging queens rather than Rybka's 19.Ng5. As you can see below Rybka took only 17 secs to select 19.Ng5 so it must have also considered it during its earlier calculations. If given more time (a little over 10 mins at d=20 in Infinite Analysis mode) Rybka still would have selected 19.Ng5 over 19.Qa4+ by a narrow margin, and this how it thought the game might continue:

Rybka considers the position after the exchange of queens as advantageous for White, and its eval started to climb, even though White extra pawn is now doubled, its Pe5 isolated, and it's hard for White to make use of the half-open f-file because of Black's LSB's command of the a6-f1 diagonal. Which Black immediately surrenders!

Setting up the usual minority attack in these types of positions, but Stockfish doesn't follow through. In spite of Black's pawn minus I prefer Black's position here. The minority attack will open up lines on the q-side and Stockfish should be able to make good use of its two bishops. White has no play on the k-side due to its doubled pawns and inability to use the half-open f-file. Still, Rybka continues to prefer its position and its eval continues to climb.

Note that 28.Nxf7 loses the exchange to 28...Bh4+, something I didn't notice at the time.

A good move by Rybka, I think, keeping the position closed. Either 34.gxf5 Bxf5 or 34.(any) fxg4 would have allowed Stockfish to open up the position somewhat and all of a sudden it's Black that has play on the f-file against White's suddenly exposed king.

Here I thought that perhaps 39...Bxf3 might have been better, Black getting rid of its bad bishop in exchange for White's knight which ought to be better in a closed position. Black would then be left with a good DSB vs. White's bad DSB. But Rybka assessed the position after 39...Bxf3 and either 40.Rxf3 or 40.Kxf3 at [+0.95], d=21, effectively the same as the game continuation. And Stockfish 2.2.2 in infinite analysis mode at d=26 didn't consider either 39...Bxf3 or the game's 39.Bd3 among its top 5 PVs, and evaluated the position at [+0.44] for all 5 PVs.

I thought that Stockfish's 42...a4 was an error, giving up the possibility of a minority attack, since now the position is entirely closed and Black has no prospects of q-side play without a pawn sac or two. White, on the other hand, theoretically has either g3-g4 or h4-h5 pawn breaks after suitable preparation so now the initiative should be in White's hands. Assuming, of course, that Rybka could figure this out. And it couldn't, so instead it goes into a series of meaningless moves which do nothing to advance its position. I call this phenomenon "engine dithering".

And this was the last pawn move for quite a while although at the time neither <kutztown46> nor myself appreciated the significance that the game would be drawn following Black's 92nd move due to the 50-move rule.

Here Rybka missed a chance to activate its bishop by 46.Bc5, although it succeeds in doing so later. White's DSB would be more active in the a3-f8 diagonal, and any exchange of DSBs should favor White since it would have a N vs. bad B in a closed position.

Unfortunately the attempt to force h4-h5 after Stockfish's 46...Be7 by either 47.Rh2 or 47.Rh1 fails against 47...Bxg5! since either rook move pins the Ph4. But even after a laborious sequence such as 47.Rdd1 Be7 48.Rh1 Rh7 49.Rh3 Bd8 50.Rah1 Bb3 51.Kg2 Bc2 52.R1h2 Be4+ 53.Kf2 Bd7 54.h5 leads to no more than equality (Stockfish, [0.00], d=30) or a miniscule edge for White (Rybka, [+0.19], d= 20) after 54...Bxg5 55.hxg6 Rxh3 56.Rxh3 Bxf4 57.gxf4 Rxg6. And, with a completely closed position and opposite colored bad bishops for each side, Stockfish's assessment seems more accurate. So there doesn't look like trying to force h4-h5 gives White any winning chances.

Finally Rybka figures out that it would be advantageous to exchange DSBs. Of course, Stockfish figures out the same thing and refuses the offer to exchange, but now White has its DSB in a more active diagonal with the d4 square free for it's knight. But Rybka doesn't consider either of these as an advantage so its eval of the position is unchanged. And, as you'll see below, it can't open up any files on the k-side as long as Stockfish has its DSB pointed at the Pg5 so it doesn't have anything meaningful to do with its rooks.

During the game I thought that Rybka could perhaps try either g3-g4 or h4-h5 to open up the position on the k-side. After 67.Rdh2 Rh5 68.Nf3 Black can no longer prevent g3-g4. But after 68...Re8 69.g4 fxg4 70.Kxg4 Bd3 Stockfish evaluates the position at [0.00], d=24 and Rybka evaluates the position at only [+0.29], d=18, quite a comedown from its current [+0.97] eval so it doesn't look like my g3-g4 idea had any merit.

Here the game was "adjourned" after Rybka made the illegal move 70.h5 since it wasn't told (by me) that Black had played 69...Rh5. But at least it vindicates my judgment that the h4-h5 pawn break was desirable even if unachievable! After the game was resumed 2 days later, Rybka's eval of the position increased from [+0.97] to [+1.02], another indication that multi-core chess engines are non-deterministic.

Another attempt by Rybka to induce Stockfish to exchange DSBs which Stockfish once again declines since 72...Bxd6 73.exd6 Kxd6 fails to 74.Rxe6+ and 75.Rxg6. So Rybka once again resorts to "meaningless rook moves" in its "engine dithering" mode. And each time that Rybka tries to force h4-h5 by doubling rooks on the h-file Stockfish prevents it by doing the same thing. But, with a pawn advantage, Rybka doesn't want to repeat the position 3 times.

Now for some unknown reason Rybka's evals started to fluctuate even though the position's characteristics had not really changed. Little did I know at the time that this may have been an indication of impending disaster.

And now, with a pawn advantage, with about 4 ½ minutes on its clock after its 90th move and only 2 more moves left before the game is declared a draw by the 50-move rule, I think that Rybka determined that a draw was unacceptable given its favorable evaluation of its position. So, in what may have been an unusual example of the horizon effect, Rybka decides to both move and sacrifice a pawn to prevent the 50-move rule draw with the least negative impact on its evaluation of the position (it's only other available pawn move, 91.g4, would have resulted in a significant advantage for Black after 91...Rxh4, and any sacrifice of the knight would presumably have been even worse). Note that after the pawn sacrifice Rybka's evaluation of the position is still favorable although, of course, not as favorable as it had been when it had a pawn advantage. I can only guess that if Rybka's eval of the position had been negative (unfavorable) then it would have preferred the draw by the 50-move rule.

At this point Rybka had about 3 minutes left in its clock. Normally it would not have been a problem for Rybka to play another 50 moves in the time remaining (making the game essentially a blitz game) although, of course, it could not have calculated as deeply and the quality of its play would have suffered. But, because I had set Ponder=ON, Rybka would have been able to use Stockfish's calculation time for its own analysis and so would likely have been able to play at a reasonable level (i.e. better than me). But the game circumstances were such that there was both a dummy in the loop (me) and a communications lag for the moves to be transmitted between opponents, adding about 10 secs/move. So Rybka didn't know that it had just lost the game on time.

And, to make matters even worse given the short amount of time that Rybka has left in its clock, Rybka now decides to open up the position in order to recapture the sacrificed pawn. So all the positions that might have remained in its hash table if the position had remained closed get flushed, and Rybka has to start the analysis anew. So the depth that it is able to calculate drops tremendously, and at low search plies Rybka is no match for Stockfish, even though it still thinks its position is favorable. Stockfish, on the other hand, thinks that its position is favorable after 96...Bxb3, [-0.28], d=26. So we have 2 "happy" engines. Interesting.

Here Rybka decides to complicate the game even further. Had it played it safe with 104.Kxg3 then the best that Stockfish was able to find for itself (d=30) was 2 draws by repetition, 104...Ba5 105.Rb5 Be1+ 106.Kf3 Rf2+ 107.Kg4 Rg2+ 108.Kf3 Rf2+ and 104...Rc4 105.Rb8 Rcxh4 106.Rxd8 Rh3+ 107.Kg2 Rh2+ 108.Kg1 Rh1+ 109.Kf2 R1h2+ 110.Kg1. Had this been played, I might have been able to make the required moves in the time available, and the game would have ended in a legitimate draw.

Here (107.Bb4 was the actual last move plated by Rybka) <kutztown46> graciously offered a draw for the second time and this time I accepted with about 2 seconds left on Rybka's clock. I still have mixed feelings about it because I feel that 91.b4 is an issue with Rybka's move determination function so, if this move would have caused Rybka to lose on time, then that would have been a legitimate way for Rybka to lose. On the other hand, Rybka had no way of knowing the approximately 10-sec/move operator/communication lag under which the game was being played. Without this lag, in the 3 seconds remaining on its clock it could have blitzed many more moves of reasonable quality, given that it could calculate during the time that Stockfish was calculating.

Thus ended probably the most controversial and drama-filled game of the 2011 Masters vs. Machines tournament, as well a probably one of the least interesting. But what might the actual game conclusion have been under a "real life" (non-analysis) situation? What might have happened if Rybka had tried b2-b4 much earlier than move 91 when it would have had much more time on its clock? To try and find out, I ran a mini-tournament (5 games, 60 minute time control) starting with the position after 107.Bb4 with Rybka 4.1 playing White and Stockfish 2.0.1 (the version that <kutztown46> was using at the time) playing Black. Here are the results. I won't bother showing the moves since they don't look all that interesting and it would make an already insufferably long post even more insufferable long.

Game 1: Drawn after 189 moves (82 additional moves) due to 50-move rule.

Game 2: Drawn after 198 moves (91 additional moves) due to 50-move rule.

Game 3: Drawn after 149 moves (42 additional moves) due to insufficient material.

Game 4: Drawn after 183 moves (76 additional moves) due to 50-move rule.

Game 5: Drawn after 217 moves (110 additional moves) due to 50-move rule.

So it looks like a draw would have been the most likely outcome if you discount the ineptness of Rybka's operator.

<Here the game was "adjourned" after Rybka made the illegal move 70.h5 since it wasn't told (by me) that Black had played 69...Rh5. But at least it vindicates my judgment that the h4-h5 pawn break was desirable even if unachievable!>.

lol !

<After the game was resumed 2 days later, Rybka's eval of the position increased from [+0.97] to [+1.02], another indication that multi-core chess engines are non-deterministic.>

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